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The impact of wave slamming indused vibration on human factors and equipment on board the SA Agulhas II

Omer, Hamza (2016-03)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: An investigation of wave slamming phenomenon was performed in the context of
human factors on-board the S.A. Agulhas II, a South African Polar Supply and
Research Vessel. Full scale vibration measurements were conducted during the
vessel’s voyage to Marion Island in 2014 and Antarctica in 2014/15. The
measurements captured vibrations in the vertical direction as per the directives of
ISO 2631-1 (1997). A questionnaire survey was conducted on both voyages to
acquire the human response to wave slamming. The study for the Marion Island
voyage focused on measurement and analysis of vibration due to slamming using
the metrics recommended by ISO 2631-1 (1997). The analysis revealed that
slamming events produce impulsive accelerations of high magnitude resulting in
broad band excitation of the vessel. The weighted r.m.s acceleration levels
resulting from slamming exceeded the comfort threshold provided by the
standard. The qualitative analysis of human response indicated that slamming not
only caused discomfort on-board but also affected work and equipment. The study
performed during the Antarctic voyage was designed to identify and correlate
measured slamming vibration data with human response and to investigate their
association. Statistical analysis, performed using Kendall’s coefficient, indicated
that slamming vibration was correlated to human complaints on-board the
S.A. Agulhas II. The highest correlation found was the cumulative Vibration Dose
Values (VDV) which proved to be the best metric amongst all others to represent
slamming vibration for human factors. In addition to that, the study evaluated the
effects of some environmental factors such as swell height and wind speed on
wave slamming. It was concluded that even moderate sea states can lead to heavy
incidences of slamming. Finally, operational deflection shapes were calculated for
the visualization of the structural response of the vessel during bow and a stern
slamming event. Time domain response and frequency response was calculated to
observe the motion of the ship as it undergoes a slamming event. The analysis
indicated that the area of impact (bow or stern) comes under severe loading
immediately. Both slamming events produce bending and twisting of the entire
structure. It was also noted that the long duration of heavy oscillations produced
by slamming may affect human comfort and performance on-board the vessel.